Alpha, omega-diols such as 1,5-pentanediol and 1,6-hexanediol are useful as chemical intermediates for the production of, e.g., agrichemicals, pharmaceuticals, and polymers. For example, α,ω-diols can be used as plasticizers and as comonomers in polyesters and polyether-urethanes. It has become increasingly desirable to obtain industrial chemicals such as α,ω-diols, or their precursors, from materials that are not only inexpensive but also benign in the environment. Of particular interest are materials which can be obtained from renewable sources, that is, materials that are produced by a biological activity such as planting, farming, or harvesting. As used herein, the terms “renewable” and “biosourced” can be used interchangeably.
Biomass sources for such materials are becoming more attractive economically versus petroleum-based ones. Although the convergent and selective synthesis of C5 and C6 carbocyclic intermediates from biomass is difficult because of the high degree of oxygenation of many components of biomass, use of such biomass-derived intermediates as feedstocks would offer new routes to industrially useful chemicals.
1,6-Hexanediol is a useful intermediate in the industrial preparation of nylon 66. 1,6-Hexanediol can be converted by known methods to 1,6-hexamethylene diamine, a starting component in nylon production. 1,6-Hexanediol is typically prepared from the hydrogenation of adipic acid or its esters or the hydrogenation of caprolactone or its oligomers. For example, in WO 2011/149339, deVries J-G, et al describe a process for the preparation of caprolactone, caprolactam, 2,5-tetrahydrofuran-dimethanol, 1,6-hexanediol or 1,2,6-hexanetriol from 5-hydroxymethyl-2-furfuraldehyde and teach that 1,2,6-hexanetriol may be hydrogenated to 1,6-hexanediol using a catalyst based on palladium, nickel, rhodium, ruthenium, copper and chromium or mixtures thereof. Further, the catalysts may be doped with one or more other elements, such as rhenium.
JP 2003-183200 teaches a method for preparation of 2,5-diethyl-1,6-hexanediol from tetrahydropyran derivatives, e.g. 2,5-dimethyltetrahydropyran-2-methanol, comprising hydrogenation of the starting material in the presence of a metal catalyst carried on an acidic support, notably 5% Pt/Al2O3 and 5% Pt/SiO2—Al2O3 at 200-240° C. Yields ranged from 40 to 61%.
There is an existing need for processes to make α,ω-diols, especially O5 and O6 α,ω-diols, and synthetic intermediates useful in the production of α,ω-diols, from renewable biosources. There is an existing need for processes to produce 1,5-pentanediol, 1,6-hexanediol, and other α,ω-diols at high yield and high selectivity from biomass-derived starting materials, including 1,2,6-hexanetriol, tetrahydrofuran-2,5-dimethanol, and 2-hydroxymethyltetrahydropyran.